Project Summary The ultimate goal of this proposal is to improve outcomes after an emergency department (ED) evaluation for suspected acute coronary syndrome (ACS). ACS includes acute myocardial infarction (AMI) and unstable angina, and is the leading cause of worldwide mortality and morbidity. Suspected ACS is the second most frequent reason for U.S. ED visits and accounts for over 7 million annual encounters. The minority (13%) of ED chest pain visits are related to ACS, and diagnosis is challenging with high clinical and medico-legal stakes. To minimize missed ACS, the American Heart Association suggests non-invasive cardiac testing (e.g. stress electrocardiogram [ECG], stress echocardiogram [echo], stress myocardial perfusion [MP], or coronary computed tomography angiogram [CCTA]) within 72 hours, after serial biomarkers have excluded AMI. Furthermore, patients with suspected ACS are often admitted to an inpatient bed or observation unit to facilitate early non-invasive testing and to mitigate the risk of dangerous complications of ischemic heart disease. Evaluation of suspected ACS is the top reason for U.S. short-stay (<48 hrs) inpatient and observation admissions, and accounts for $3-10 billion in hospital costs per year. However, there is no evidence that early non-invasive testing or hospital based evaluation benefits patients. Current use of early non-invasive tests increases rates of invasive coronary angiography and revascularization without reducing AMI risk. The potential benefits of hospital admission in low-risk patients appear to be marginal (<0.2% cardiac event rate during admission). The widely varying rates of non-invasive testing (6x difference between top and bottom quartile hospitals) and hospitalization (7x difference between top and bottom quartile hospitals) for suspected ACS suggest pervasive uncertainty about the optimal approach. Using prospective observational data on ~170,000 patient encounters within an integrated health system, we will assess five early diagnostic (stress ECG, stress echo, stress MP, CCTA, or NO non-invasive testing) and three disposition (inpatient, observation, discharge) strategies: Aim 1. Compare 30-day outcomes of early diagnostic testing strategies for suspected ACS Aim 2. Compare 30-day outcomes of disposition strategies for suspected ACS Aim 3. Assess whether pre-test risk affects the comparative effectiveness of early diagnostic and disposition strategies for suspected ACS Aim 4. Compare cost-effectiveness of early diagnostic and disposition strategies for suspected ACS The Aims address questions fundamental to any evaluation for suspected ACS: 1. What test if any is needed? 2. Is admission beneficial? 3. How does patient pre-test risk modify management? Aim 4 will inform policy makers and payers about the comparative value of different strategies.